The present invention relates to certain porous metallic structures and processes for making same. The invention particularly relates to metallic structures having very small pore sizes being of uniform and interconnected porosity. The porous metallic structures have utility, for example, as metal membranes or filters.
Broadly described, the porous metallic structures are produced by mixing at least two metals having significantly different electrochemical activities, according to predetermined proportions, to form a multi-metallic alloy; contacting the alloy with an electrolyte; and applying an electrochemical potential between the metal and the electrolyte wherein the alloy acts as an anode until all or a portion of the more electrochemically active metal is dissolved from the alloy leaving porous metal. The porous metal in another embodiment of the present invention is heat annealed i.e. coarsened to increase the pore size and mechanical stability of the porous metal. The structures are produced with uniform porosity in pore sizes ranging from about 3 nanometers to 10 micrometers. The porous structure can be produced in thicknesses ranging from 0.0001 to 10 mm. Depending upon the elemental composition of the membrane, the volume fraction of porosity attainable in the structures ranges from 30-80% and all of the porosity is substantially all interconnected. Membranes prepared in this way are mechanically tough, chemically inert, and heat resistant (e.g. thermally sterilizable). Such a membrane may be employed as a filter to separate particles, of size down to the molecular level, from gases and liquids.